U.S. patent number 4,350,354 [Application Number 06/214,908] was granted by the patent office on 1982-09-21 for self-levelling suspension system for motor-vehicles.
This patent grant is currently assigned to Centro Ricerche Fiat S.p.A.. Invention is credited to Giulio Dotti, Renzo Masoero.
United States Patent |
4,350,354 |
Dotti , et al. |
September 21, 1982 |
Self-levelling suspension system for motor-vehicles
Abstract
A suspension system for motor vehicles of the type designed to
maintain automatically the horizontal attitude of a motor vehicle
with variations in loads on the front suspensions and on the rear
suspensions comprises two hydraulic cylinders interposed between
the springs of the rear suspensions and the suspended masses in
correspondence with the rear axle of the motor vehicle. Each
hydraulic cylinder incorporates a distribution valve comprising a
slide valve subject at one of its ends to the pressure within the
hydraulic cylinder and its opposite end to the pressure transmitted
by a hydraulic pump by means of a control valve which is responsive
to the subsidence of the front suspensions. The said distribution
slide valve is designed to connect the hydraulic cylinder to
exhaust when pressure is transmitted from the said control valve
and to connect the internal chambers of the hydraulic cylinder to a
pipe directly connected to the outlet of the hydraulic pump when
there is pressure inside the hydraulic cylinder. A spring acting as
a sensor element of variations in length of the hydraulic cylinder
is designed to return the slide valve to one of its conditions of
equilibrium, in which the internal chamber of the hydraulic
cylinder is isolated, when the motor vehicle becomes situated in a
horizontal attitude.
Inventors: |
Dotti; Giulio (Milan,
IT), Masoero; Renzo (Turin, IT) |
Assignee: |
Centro Ricerche Fiat S.p.A.
(Turin, IT)
|
Family
ID: |
11298876 |
Appl.
No.: |
06/214,908 |
Filed: |
December 10, 1980 |
Foreign Application Priority Data
|
|
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|
|
Jan 7, 1980 [IT] |
|
|
67012 A/80 |
|
Current U.S.
Class: |
280/6.159;
267/187; 280/124.162 |
Current CPC
Class: |
B60G
17/0272 (20130101); B60G 17/0277 (20130101); B60G
17/033 (20130101); B60G 21/06 (20130101); B60G
2202/12 (20130101); B60G 2202/135 (20130101); B60G
2500/30 (20130101); B60G 2204/11 (20130101); B60G
2204/124 (20130101); B60G 2204/42 (20130101); B60G
2500/02 (20130101); B60G 2500/20 (20130101); B60G
2202/413 (20130101) |
Current International
Class: |
B60G
17/033 (20060101); B60G 17/027 (20060101); B60G
17/02 (20060101); B60G 21/00 (20060101); B60G
21/06 (20060101); B60G 017/00 () |
Field of
Search: |
;280/6H,6.1,104,714
;267/11R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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1260844 |
|
Jan 1972 |
|
GB |
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1337241 |
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Nov 1973 |
|
GB |
|
Primary Examiner: Song; Robert R.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas
Claims
We claim:
1. Suspension system for motor vehicles, of the type
comprising:
means for sensing subsidence of the front suspensions of the motor
vehicle,
means for sensing subsidence of the rear suspensions of the motor
vehicle,
actuator means to vary the level of the suspended masses in
correspondence with the rear axle of the motor vehicle, and
control means, controlled by the said sensor means, designed to
cause the operation of the said actuator means in order to maintain
automatically the horizontal attitude of the motor vehicle upon
variation in the loads on the front suspensions and on the rear
suspensions, wherein
(a) the said system comprises at least one hydraulic cylinder
interposed between the springs of the rear suspension and the
suspended masses of the motor vehicle, designed to function at the
same time as actuator member and as the member for sensing the
subsidence of the rear suspensions, the said hydraulic cylinder
comprising two members, fixed respectively to the springs of the
rear suspensions and to the suspended masses of the motor vehicle,
which define between them an internal chamber,
(b) the said system further comprises a tank and a hydraulic pump
the inlet to which is connected to the tank and the outlet from
which is connected to a first input of the said hydraulic cylinder
through a first pipe, and to a second input of the said hydraulic
cylinder through a second pipe,
(c) the means for sensing the subsidence of the front suspensions
comprise a control valve for controlling the pressure existing in
the said second pipe, the said control valve comprising a movable
control member designed to move as a function of the subsidence of
the front suspensions in order to cause an increase in the pressure
in the second pipe as the subsidence of the front suspensions
increase.
(d) the control means comprise a distribution valve incorporated in
one of the two members forming the hydraulic cylinder and including
a slide valve subject at one of its ends to the pressure
transmitted through the said second input and at its opposite end
to the pressure existing in the internal chamber of the hydraulic
cylinder; the said slide valve being movable between a first end
position, corresponding pressure being transmitted through the said
second input, in which the internal cavity of the hydraulic
cylinder is connected to exhaust, so as to cause retraction of the
hydraulic cylinder, and a second end position, corresponding to
there being pressure in the internal chamber of the hydraulic
cylinder, in which the said internal chamber is put in
communication with the said first input, so as to cause extension
of the hydraulic cylinder,
(e) the control means further comprise a spring, acting as the
member for sensing the variation in the length of the hydraulic
cylinder, interposed between the slide valve associated with one of
the two members forming the hydraulic cylinder and the other member
of the hydraulic cylinder, the said spring being designed to bring
the slide valve back into one of its positions of equilibrium in
which the internal chamber of the hydraulic cylinder is isolated,
when the vehicle becomes situated in horizontal attitude.
2. Suspension system according to claim 1, wherein the said system
comprises twohydraulic cylinders interposed between the springs of
the rear suspension and the suspended masses of the motor vehicle
respectively.
3. Suspension system according to claim 1, wherein the hydraulic
cylinder comprises two substantially cup-shaped elements assembled
slidingly one inside the other with their internal cavities facing
each other.
4. Suspension system according to claim 1, wherein the said control
valve is interposed in a third pipe which connects the second pipe
to the tank, the said control valve being designed to control the
quantity of fluid which is discharged from the second pipe into the
tank through the said third pipe, so as to control the pressure
existing in the second pipe.
5. Suspension system according to claim 4, wherein in the first end
position of the slide valve, the internal chamber of the hydraulic
cylinder communicates with the tank by means of the second input,
the second pipe, the control valve and the third pipe.
6. Suspension system according to claim 1, wherein in the first end
position of the slide valve, the internal chamber of the hydraulic
cylinder communicates with a third input of the hydraulic cylinder
which is connected to the tank.
7. Suspension system according to claim 1, wherein the control
valve comprises a non-return valve, comprising a valve seat, an
obturator and elastic means designed to press the obturator against
the valve seat, the said movable control member being mechanically
connected to a stabilizing bar of the front wheels so as to cause
an increase in the load of the said elastic means as the subsidence
of the front suspensions of the motor vehicle increases.
8. Suspension system according to claim 7, wherein the said
non-return valve comprises a body, two internal chambers which
communicate respectively with the sections of the third pipe
arranged upstream and downstream of the said valve, the said valve
seat comprising the edge of an aperture made in a baffle which
separates the two internal chambers from each other, the valve
obturator and the elastic means designed to press the obturator
against the valve seat comprising respectively a ball element
arranged in the internal chamber which communicates through the
third pipe with the tank and a helical spring interposed between
the base element and the moveable control member.
9. Suspension system according to claim 8, wherein the movable
control member forming part of the control valve comprises a member
assembled slidingly in the body of the said valve and having one
end protruding outside the said body, the said end being
mechanically connected to a transverse lever fixed to the central
section of the said stabilizing bar.
10. Suspension system according to claim 1, wherein the hydraulic
cylinder is provided with stop means designed to maintain the slide
valve in its first end position when the internal chamber of the
hydraulic cylinder is not filled with fluid.
Description
The present invention relates to suspension systems for motor
vehicles, of the type comprising:
means for sensing subsidence of the front suspensions of the motor
vehicle,
means for sensing subsidence of the rear suspensions of the motor
vehicle,
actuator means to vary the level of the suspended masses in
correspondence with the rear axle of the motor vehicle, and
control means, controlled by the said sensor means, designed to
cause the operation of the said actuator means in order to maintain
automatically the horizontal attitude of the motor vehicle upon
variations in the loads on the front suspensions and on the rear
suspensions.
Suspension systems of the type specified above are described and
illustrated for example in British Pat. Nos. 1,337,241 and
1,260,844.
The object of the present invention is to provide a suspension
system for motor vehicles of the type specified above which is of
reliable and simple construction and which has, in particular, a
smaller number of parts.
In order to achieve this object, the present invention provides a
suspension system for motor vehicles of the type specified at the
beginning, characterised by the following combination of
characteristics:
(a) the said system comprises at least one hydraulic cylinder,
interposed between the springs of the rear suspension and the
suspended masses of the motor vehicle, which is designed to
function at the same time as the actuator member and as the member
for sensing the subsidence of the rear supensions, the said
hydraulic cylinder comprising two members, fixed to the springs of
the rear suspensions and to the suspended masses of the motor
vehicle respectively, which define between them an internal
chamber,
(b) the said system further comprises a tank and a hydraulic pump
the inlet to which is connected to the tank and the outlet from
which is connected to a first input of the said hydraulic cylinder
through a first pipe and to a second input of the said hydraulic
cylinder through a second pipe,
(c) the means for sensing the subsidence of the front suspensions
comprise a control valve for controlling the pressure existing in
the said second pipe, the said control valve comprising a movable
control member designed to be displaced as a function of the
subsidence of the front suspension, in order to cause an increase
in the pressure in the second pipe as the subsidence of the front
suspensions increases,
(d) the control means comprise a distribution valve incorporated in
one of the two members forming the hydraulic cylinder and including
a slide valve subject at one of its ends to the pressure
transmitted through the said second input and at its opposite end
to the pressure exising in the internal chamber of the hydraulic
cylinder, the said slide valve being displaceable between a first
end position, corresponding to the situation where pressure is
transmitted through the said second input, in which the internal
chamber of the hydraulic cylinder is connected to exhaust so as to
cause retraction of the hydraulic cylinder, and a second end
position, corresponding to the situation where there is pressure in
the internal chamber of the hydraulic cylinder, in which the said
internal chamber is put in communication with the said first input,
so as to cause extension of the hydraulic cylinder,
(e) the control means further comprise a spring acting as the
element for sensing the variation in length of the hydraulic
cylinder, interposed between the slide valve associated with one of
the two elements forming the hydraulic cylinder and the other
element of the hydraulic cylinder, the said spring being designed
to bring the slide valve back into one of its positions of
equilibrium, in which the internal chamber of the hydraulic
cylinder is isolated, when the vehicle becomes situated in a
horizontal attitude.
The present invention will now be described with reference to the
accompanying drawings, supplied purely by way of non-limitative
example, in which:
FIG. 1 is a diagrammatic perspective view of a suspension system
according to the present invention,
FIG. 2 is a sectional diagrammatic view of a hydraulic cylinder
forming part of the system of FIG. 1,
FIGS. 3, 4 show a control valve forming part of the system of FIG.
1 in two different working conditions,
FIGS. 5, 6 show the principle of operation of the suspension system
according to the present invention, and
FIG. 7 is a variant of FIG. 2.
In FIG. 1, reference numeral 1 indicates in its entirety a
suspension system associated with a vehicle comprising two front
wheels 2 and two rear wheels 3. Associated with the front wheels 2
are two suspension springs 4 and a stabilizing torsion bar 5.
Associated with the rear wheels 3 are two suspension springs 6 and
two shock absorbers 7. Reference numeral 8 indicates fragmentary
parts of the suspended mass of the motor vehicle.
With each of the springs 6 of the rear suspension there is
associated a hydraulic cylinder 9 (see FIG. 2) which is interposed
between the corresponding spring 6 and the suspended mass 8 of the
motor vehicle. The hydraulic cylinder 9 comprises two elements
10,11, susbtantially cup-shaped, assembled slidingly one inside the
other with their cavities facing each other, so as to define an
internal chamber 12. In the base portion of the cup element 10
there is incorporated a distribution valve 13 comprising a slide
valve 14 assembled slidingly inside a cavity 15 which extends
coaxially with the hydraulic cylinder 9 from the surface of the
base portion of the cup element 10 which is facing the internal
chamber 12.
The cavity 15 communicates through a first inlet 16 with a first
pipe 17 connected to the outlet of a hydraulic pump 18. The input
to the pump 18 is connected to a tank 19. The cavity 15 also
communicates through a second inlet 20 with a second pipe 21
connected to the output of the hydraulic pump 18. The second pipe
21 also communicates through a third pipe 22 with the tank 19.
Finally, the cavity 15 inside which the slide valve 14 is assembled
slidingly also communicates, with a pipe 23 which leads to the
internal chamber 12 of the hydraulic cylinder.
The slide valve 14 is displaceable between a first end position,
corresponding to the abutment of its lower surface against a stop
ring 24 and a second end position corresponding to the abutment of
the upper surface of the valve against the upper end surface of the
cavity 15.
When the slide valve 14 is situated in its first end position, the
second inlet 20 communicates through the duct 23, with the internal
chamber 12. When, however, the valve 14 is situated in its second
end position, the internal chamber 12 communicates instead with the
first inlet 16.
The cup element 10 is secured to a support 8a fixed to the
suspended masses 8 of the motor vehicle by means of a ring nut 25
secured onto the base portion of the elemtn 10. The cup element 11
is provided instead with an annular flange 11a which rests on the
upper end of the spring 6. Between the slide valve 14 and the base
of the cup element 11 there is axially interposed a helical spring
26, the function of which will become apparent in due course. In
FIG. 2, the slide valve 14 is shown in an intermediate position of
equilibrium between its two end positions, in correspondence with
which the internal chamber 12 of the hydraulic cylinder 9 does not
communicate with the first inlet 16 nor with the second inlet
20.
In the duct 22 (see FIG. 1) which puts the duct 21 in communication
with the tank 19, there is interposed a control valve 27 comprising
a body 28, fixed to the suspended masses 8 of the motor vehicle,
inside which are defined two chambers 29, 30 which communicate with
each other by means of an aperture 31 made in a baffle 32 which
separates these chambers from each other. The chamber 29
communicates with the pipe 21, whilst the chamber 30 communicates,
through the pipe 22 with the tank 19. The edge of the aperture 31
functions as a seat for a ball obturator 33 which is pressed
against it by a helical spring 34. The helical spring 34, which is
arranged inside the chamber 30, acts at one of its ends on the ball
obturator 33 by means of a cap 35, and at its other end against a
seat 36 made at the end of an element 37 assembled slidingly in the
body 28 and having one end protruding outside the latter. This end
of the element 37 co-operates with a lever arm 38 which is fixed to
the stabilizing bar 5 and which rotates around the axis 39 of this
bar with the variation in the subsidence of the front suspensions
of the motor vehicle.
In the section of the pipe 21 comprised between the output of the
hydraulic pump 18 and the point at which this duct communicates
with the pipe 22 there is interposed a constriction 40 for the
purpose of preventing the pressure in the pipe 22 being influenced
by the pressure existing in the pipe 17.
Reference numeral 41 indicates a valve interposed in a pipe 42
which puts the output of the hydraulic pump 18 in communication
with the tank 19.
The operation of the suspension system described above is as
follows:
When the motor vehicle is situated in horizontal attitude, the
slide valve 14 of each hydraulic cylinder 9 is situated in its
equilibrium position shown in FIG. 2.
Supposing that in these conditions an increase occurs in the load
acting on the front suspensions of the motor vehicle, this increase
will cause subsidence of the front suspensions and, as a result, a
lowering of the suspended masses 8 of the motor vehicle with
respect to the front wheels 2. The body 28 of the control valve 27
and the stabilizing bar 5 lower at the same time as the suspended
masses 8 with respect to the wheels of the motor vehicle. This
lowering is therefore accompanied in addition by a rotation of the
central section of the stabilizing bar 5 around its axis 39. This
rotation causes a corresponding rotation of the lever arm 38 fixed
with the stabilizing bar, which is thus brought from the position
shown in FIG. 3, for example into the position shown in FIG. 4. The
rotation of the lever arm 38 causes the retraction of the element
37 inside the chamber 30 of the valve 27, with a resulting increase
the pre-load of the helical spring 34.
When the motor vehicle is in a horizontal attitude (in this
condition the control valve 27 is situated in the position shown in
FIG. 3) the fluid supplied by the hydraulic pump 18 flows through
the pipe 21 and the pipe 22 into the internal chamber 29 of the
control valve 27 and from here passes into the chamber 30 after
having caused the withdrawal of the ball obturator 33 by overcoming
the reaction of the spring 34. From the chamber 30 the fluid then
returns into the tank 19 through the pipe 22. Since, with the
increase in the subsidence of the front suspensions, the pre-load
of the helical spring 34 increases through the effect of the
rectraction of the element 37 inside the chamber 30, the fluid
supplied by the pump 18 must overcome an even greater reaction
force in order to cause the withdrawal of the valve obturator 33 as
the subsidence of the front suspensions increases. It is clear,
therefore, that as this subsidence increases, so the pressure
increases in the section of the pipe 21 which is arranged
downstream of the point which communicates with the pipe 22.
Finally, to the second input 20 of each hydraulic cylinder 9 a
pressure is transmitted which is a function of the subsidence of
the front wheels of the motor vehicle.
The slide valve 14 associated with each hydraulic cylinder 9 would
tend to be displaced downwards, towards its first end position,
through the effect of the action of the pressure transmitted
through the input 20 and of the action of the helical spring 26. On
the other hand the slide valve 14 is thrust upwards by the pressure
existing in the internal chamber 12.
Supposing that the subsidence of the front suspensions is such that
it causes a sufficient increase in the pressure transmitted to the
inlet 20 through the pipe 21, the slide valve 14 associated with
each hydraulic cylinder 9 moves downwards putting the internal
chamber 12 of the hydraulic cylinder in communicaton with the inlet
20. Since the system is designed in such a way that the pressure
transmitted to the inlet 20 is always less than the pressure
existing inside the chamber 12, the connection between the inlet 20
and the chamber 12 causes the discharge of the fluid contained in
the latter through the duct 23 and the inlet 20, the pipe 21, and
the pipe 22 into the tank 19. As a result, the hydraulic cylinders
9 retract, as a result of which the lowering of the front part of
the motor vehicle which had suffered a deviation from the
horizontal attitude is followed by a corresponding lowering of the
rear part of the motor vehicle.
Naturally, as each hydraulic cylinder retracts, the action exerted
by the spring 26 on the slide valve 14 and tending to push this
valve downwards diminishes. The system is designed in such a way
that when the retraction of the hydraulic cylinders 9 is such that
it establishes the horizontal attitude of the motor vehicle, each
slide valve 14 returns to its position of equilibrium, interrupting
the communication of the chamber 12 with the tank 19.
In this phase of operation therefore each hydraulic cylinder 9
functions as an actuator member designed to change the level of the
suspended masses on the rear suspension of the motor vehicle so as
to maintain automatically the horizontal attitude of the said
vehicle.
The helical spring 26 functions, in some respect, as the member for
sensing the variation in the length of the hydraulic cylinder 9 and
has the task of acting in such a way that the slide valve 14
returns to its position of equilibrium when the motor vehicle
becomes situated in the horizontal attitude.
Supposing now that the motor vehicle deviates from its horizontal
attitude as a result of an increase in the load on the rear
suspensions, this increase tends to cause the two cup elements 10,
11 forming each hydraulic cylinder 9 to approach each other in the
axial direction. The increase in pressure inside the chamber 12
caused by this approaching movment tends to move the slide valve 14
upwards its second end position.
If the increase in the load on the rear suspension is such that it
causes inside the chamber 12 a pressure sufficient to bring the
slide valve 14 into its second end position, overcoming the action
of the helical spring 26, the internal chamber 12 is put in
communication with the output of the hydraulic pump 18 through the
inlet 16 and the pipe 17.
In this phase of operation, as may be seen, each hydraulic cylinder
9 functions as a member for sensing the subsidence of the rear
suspensions.
Once put in communication with the output of the pump 18, the
chamber 12 receives the fluid supplied by the said pump, as a
result of which the two cup elements 10,11 tend to move away from
each other axially, causing a lengthening of the hydraulic cylinder
9.
The lowering of the rear part of the motor vehicle which had given
rise to a deviation of the vehicle from the horizontal attitude is
thus immediately followed by a raising of the said rear part of the
motor vehicle through the effect ofthe lengthening of the hydraulic
cylinders 9 interposed between the suspension springs 6 and the
suspended masses 8 of the motor vehicle.
In this phase of operation the hydraulic cylinders 9 function, as
already described above, as actuator members designed to cause a
variation in the level of the rear part of the motor vehicle.
It may be concluded, therefore, that, in the system according to
the present invention, the means for sensing subsidence of the
front suspensions comprise the control valve 27, whilst the
hydraulic cylinders 9 are used at the same time both as means for
sensing subsidence of the rear suspensions, and as actuator means
for effecting variation in the level of the suspended masses in
correspondence with the rear axle of the motor vehicle. The helical
spring 26 associated with each hydraulic cylinder 9 functions,
finally, as the member for sensing the variation in the length of
the hydraulic cylinder and is intended to re-establish the
condition of equilibrium when the horizontal attitude of the
vehicle is regained.
For the correct functioning of the suspension system described
above it is necessary that the slide valve 14 associated with each
hydraulic cylinder 9 should become situated in its position of
equilibrium when the motor vehicle regains its horizontal
attitude.
In FIG. 6 the reference numeral 4a indicates a spring which
represents the springs 4 of the front supension of the motor
vehicle. The rigidity of the spring 4a corresponds therefore to the
sum of the rigidities of the springs 4 of the front suspension. The
reference numeral 6a indicates a spring corresponding to the
springs 6 of the rear suspension of the motor vehicle. The rigidity
of the spring 6a corresponds therefore to the sum of the rigidities
of the springs 6 of the rear suspension. In the drawings there is
also shown diagrammatically a hydraulic cylinder 9 associated with
the spring 6a.
The springs 4a and 6a are represented by dashed lines in their
configuration corresponding to the condition in which the motor
vehicle is empty, and by continuous lines in their configuration
corresponding to the condition of the vehicle subjected to a
general load on the front axle and on the rear axle.
By y.sub.O is indicated the distance between the annular flange 11a
and the support 8a associated with the hydraulic cylinder 9 when
the motor vehicle is in its empty condition and in a horizontal
attitude.
By F.sub.AO and by F.sub.pO are indicated the loads acting on the
springs 4a, 6a respectively in the empty condition of the
vehicle.
By F.sub.A and F.sub.p are indicated the loads acting on the
springs 4a, 6a respectively in a generally loaded condition of the
vehicle.
By y.sub.A and y.sub.p are indicated the compressive strokes of the
springs 4a and 6a respectively corresponding to the transition from
the empty condition to the loaded condition of the vehicle.
Finally, by y.sub.C is indicated the stroke of the hydraulic
cylinder 9 corresponding to the loaded vehicle condition.
Supposing that in the empty vehicle condition corresponding to the
application of the loads F.sub.AO and F.sub.pO the vehicle is
situated in horizontal attitude, the condition for horizontality
under any other condition of load is expressed by the following
relation:
If k.sub.A and k.sub.p are the rigidities of the springs 42 and 52
respectively, the magnitudes of the strokes y.sub.A and y.sub.p are
expressed by the following relations: ##EQU1##
Substituting the relations (2) and (3) in the relation (1), an
expression is obtained for the stroke y.sub.C which the hydraulic
cylinder 9 must make in order to maintain the horizontal attitude
of the motor vehicle in any condition of load on the suspensions:
##EQU2##
In order for the slide valve 14 (see FIG. 5) associated with each
hydraulic cylinder 9 to be situated in its position of equilibrium
shown in FIG. 2, it is necessary for the following relation to be
satisfied:
where:
A is the cross-sectional area of the slide valve 14;
P.sub.A is the pressure transmitted to the second inlet 20 of the
hydraulic cylinder 9;
p.sub.p is the pressure existing in the internal chamber 12 of the
hydraulic cylinder 9;
f.sub.O is the pre-load of the spring 26 associated with each
hydraulic cylinder in correspondence with the condition y.sub.C
=O;
k.sub.M is the rigidity of the springs 26.
The magnitude of the pressure P.sub.A transmitted to the inlet 20
associated with each hydraulic cylinder 9 by means of the valve 27
and the pipes 22,21 is expressed by the following relation:
##EQU3## where:
p.sub.AO is the pressure transmitted to the inlet 20 when the front
suspensions are subject to the load F.sub.AO,
L.sub.B is the length of the arm of the appendage 37 with respect
to the axle 39 (see FIGS. 3,4),
k.sub.V is the rigidity of the spring 34 associated with the valve
27,
b is the cross-sectional area of the aperture 31.
Putting L.sub.V =.epsilon. and taking into account the fact that
p.sub.p =F.sub.p/s, where S is the cross-sectional area of the
hydraulic cylinder (5) (see FIG. 2), if the expression (6) is
substituted in the expressions (5), the following relation is
obtained: ##EQU4##
This relation expresses the condition which must be satisfied in
order for the slide valve 14 associated with each hydraulic
cylinder 9 to be situated in its position of equilibrium shown by
FIG. 2.
If it is desired to have the motor vehicle situated in horizontal
attitude when the slide valve 14 is in its position of equilibrium,
it is necessary that the expressions (4) and (7) be satisfied
simultaneously.
Substituting the expression (4) in the expression (7), the
following relation is obtained: ##EQU5##
In conclusion, if it is desired to have the slide valve 14 situated
in its position of equilibrium when the motor vehicle regains its
horizontal attitude, it is necessary to arrange the system
described above in such a way that the relation (8) is
satisfied.
Since this relation is always satisfied, however the loads F.sub.A
and F.sub.p vary, it is sufficient that the coefficients which
appear in the relation (8) are zero.
The following three relations then derive from the relation (8):
##EQU6##
For the correct functioning of the system described above it is
necessary, finally, that the pressure p.sub.A transmitted to the
inlet 20 of each hydraulic cylinder (9) should always be less than
or at most equal to the pressure p.sub.p existing in the internal
chamber 12 of the hydraulic cylinder 9. This condition must
necessarily be satisfied if it is desired that when the slide valve
14 is situated in its first end position, the internal chamber 12
of the hydraulic cylinder (9) is connected to exhaust through the
pipe 20.
In the following treatment it is supposed that the condition in
which the ratio p.sub.A p.sub.p assumes its maximum value is that
of an empty vehicle at maximum deceleration.
Supposing that F*.sub.AO and F*.sub.PO are the loads acting on the
front suspension and on the rear suspension in the condition
defined above, the relation p.sub.A .ltoreq.p.sub.p becomes:
##EQU7##
In order for the system according to the present invention to
function correctly in the manner which has been described above, it
is therefore necessary that the relations (9), (10), (11) and (12)
be satisfied.
FIG. 7 illustrates a variant of the hydraulic cylinder 9 shown in
FIG. 2.
In the example of embodiment shown in FIG. 7, the cup element 10
forming part of the hydraulic cylinder 9 has a head 10a in which
are formed the first inlet 16 intended to be connected to the pipe
17, the second inlet 20, intended to be connected to the pipe 21
and a third inlet 50 intended to be connected directly to the tank
19. Therefore, in the case where a hydraulic cylinder 9 of the type
shown in FIG. 7 is used, the system shown in FIG. 1 includes a
further pipe for the connection of the inlet 50 to the tank 19.
The inlet 16 communicates with the cavity 15 in which the slide
valve is slidingly assembled 14 by means of an axial duct 16a and a
radial duct 16b. The inlet 20 communicates with the chamber 15 by
means of an axial duct 20a which leads to the upper end wall of the
chamber 15. The inlet 50 communicates with the chamber 15 by means
of an axial duct 50a and a radial duct 50b.
The slide valve 14 is provided with a circumferential groove which
defines together with the wall of the cavity 15 an annular chamber
14a. The chamber 14a communicates with the internal chamber 12 of
the hydraulic cylinder 9 by means of ducts 14b made inside the
slide valve 14.
The cup element 11 forming part of the hydraulic cylinder has an
axial cylinder appendage 51 protruding inside the chamber 12 from
the head 11a of the element 11. The ends of the helical spring 26
are secured in correspondence with grooves 52, 53 made in an axial
cylindrical appendage 54 fixed to the slide valve 14 and in the
axial appendage 51 extending from the head 11a respectively. The
free ends of the appendages 51,54 are situated in contact with each
other when the chamber 12 is not filled with fluid coming from the
pump 18, during the periods of non-utilization of the suspension
system described above. In this condition (shown in FIG. 7) the
slide valve 14 is maintained by the appendage 51 in its second end
position, corresponding to the communication of the first inlet 16
with the internal chamber 12. In this manner, when the pump 18 is
activated to deliver fluid to the internal chamber 12 of each
hydraulic cylinder 9, the fluid which reaches the inlet 16 may get
as far as the chamber 12. When sufficient pressure is reached
inside the chamber 12, the consequent raising of the cup element 10
with respect to the cup element 11 makes it possible for the slide
valve 14 to be brought into its intermediate position of
equilibrium corresponding to the horizontal attitude of the motor
vehicle.
* * * * *